How to get preseeded proxy setting from debconf?

[Josef Wolf]

Hello!

While installing, debian-installer asks for a proxy to use to fetch
additional packages.  I have preseeded this question with:

  d-i mirror/http/proxy string http://proxy.do.main:1234

This setting is configured into apt, so apt-get works seamlessly.
The setting is also recorded in /var/log/installer/cdebconf/questions.dat.

Unfortunately, no other packages get this setting configured, so
apt-get is virtually the _only_ application that happens to use the
proxy.

I'd like to fix that in an automated way.  So I've done

  for owner in `debconf-show --listowners` ; do
    echo $i
    debconf-show $owner
    echo
  done | grep proxy

to find out the setting.  But for some reason, debconf seems not to
know about this setting.  Any ideas where it gets lost?